In well drilling and production operations, equipment for running and retrieving multiple pipe strings is typical. In order to grip the tubulars for the purpose of axially rotating or securing the tubulars against axial rotation, a gripping type device is used. Many of these devices utilize gripping means which cause surface or structural damage to the tubular being gripped. Even minor damage to the surface of the tubular, may result in a premature leak or rupture.
Prior art devices which have reduced the tendency to damage the tubulars being gripped have been relatively complicated in design, and too large for dual string operations. In order to install these devices in a dual string arrangement, the tubulars must be deflected from their normal centerline. This results in damage to the tubular members.
Hitherto, prior art means for gripping tubular members has been by the use of gripping means which result in damage to the surface of the tubular member, or a complicated design which may result in pipe damage when installed in a dual string arrangement. Therefore, the prior art has not disclosed a grip, which does not score or damage the outside diameter of the pipe, nor which may be easily used with an identical second device in a dual string application.
For the foregoing reasons, there is a need for a new improved friction grip for gripping tubular goods by means of frictional engagement only.
For the foregoing reasons, there is a need for a new improved friction grip with a flexible gripping surface to compensate for manufacturing irregularities of tubulars.
For the foregoing reasons there is a need for a new improved friction grip with lowered gripping (radial) forces per unit of contact area.
For the foregoing reasons there is a need for a new improved friction grip which provides a simpler and lower maintenance internal structural design.
For the foregoing reasons, there is a need for a new improved friction grip that can easily be used in a dual string application without damage to or deflection of the tubular member, or which requires modification of traditional torque transfer equipment.
The new improved friction grip apparatus, for gripping tubular goods, without causing surface or structural damage, is characterized by a generally cylindrical outer sleeve; a flexible liner disposed inside of the outer sleeve; an annular bladder-like structure disposed within the flexible liner; an inner sleeve disposed within the flexible liner; a torque transmitting bushing for the distribution of rotary forces throughout the bladder-like structure; a means for introducing fluid pressure into the bladder-like structure; anti-extrusion rings to prevent deformation of the liner into the annular space between the outer sleeve and tubular member within the new improved friction grip; and, an inner lining or coating of friction enhancing material.
The new improved friction grip is installed around the circumference of the tubular to be gripped, then a controlled amount of fluid pressure is introduced into the bladder-like structure. Initial introduction of pressure causes the flexible liner to expand radially inward and drive the friction sleeve and inner face of the flexible liner into contact with a tubular member.
Further introduction of fluid pressure into the bladder causes the flexible liner and friction sleeve to thrust against the tubular with increased radial pressure. By controlling the amount of fluid pressure introduced into the bladder the lowest amount of radial force necessary to produce adequate torquing (frictional force) can be selected.
Once the new improved friction grip has been engaged with fluid pressure, rotary torque is applied to the outer sleeve by various conventional means (tongs, pipe wrenches, etc.). The torque applied to the outer sleeve is transmitted through the outer sleeve, torque transmitting bushing, and flexible liner to the gripped pipe.
When the tubular work piece has been sufficiently tightened, external torque is removed from the new improved friction grip and fluid pressure in the bladder-like structure released. Upon release of the fluid pressure the flexible liner elastically retracts from contact with the work piece and the new improved friction grip is removed. The new improved friction grip may be made in two (or more) hingedly connected sections to facilitate installation on, or removal from, tubular goods.